With the rapid development of the wireless communication technology, people's demand for the communication through the user equipments (UEs), e.g., smart phones, tablet computers, etc., increases correspondingly. To meet users' requirements, new-generation mobile communication systems have been proposed one after the other, e.g., a long term evolution (LTE) communication system, a worldwide interoperability for microwave access (WiMAX) communication system and the like. In those mobile communication systems, the user equipment would perform a random access procedure to obtain radio resources for subsequent data transmission with the base station when it is just turned on, when its connection is interrupted or when it lost synchronization with the base station. During the random access procedure, the user equipment will transmit a random access request message on a specific channel learned from the broadcast message transmitted by the base station. The user equipment randomly selects a preamble from a plurality of preambles defined by the communication system, and generates the random access request message based on the selected preamble.
However, in recent years, except for common UEs, more and more wireless devices having the communication function of the mobile communication system have been manufactured, for example, internet of things (IoT) devices, wireless devices conforming to the machine type communication (MTC) specification or the like. Accordingly, when a large number of wireless devices (i.e., UEs, IoT devices, MTC devices, and wireless devices having the communication function of the mobile communication system) perform the random access procedure at the same time, it is easy for some wireless devices to select the same preamble since they all randomly select one preamble from the same preamble set, and consequently, the collision of preamble occurs among the random access request messages transmitted by those wireless devices.
In a case where the collision probability of preamble continuously increases with the increase of wireless devices, the wireless devices should randomly reselect a preamble once the collision of preamble occurs among the random access procedure and retransmit a random access request message. Those operations of randomly reselecting a preamble and retransmitting a random access request message will increase the time to successfully achieve the random access procedure, or even the wireless devices will stop the random access procedure when the number of failure reaches a system limit. As a result, the wireless devices may be unable to transmit data with the base, and radio resources in the base station may be idle as not being used.
Moreover, various wireless devices have different data transmission requirements. The UEs usually require instant data transmission, while part of IoT devices and MTC devices do not require instant data transmission. Therefore, the serious preamble collision will cause the UEs unable to instantly obtain resources for data transmission so as to make a bad impression on users.
Accordingly, how to provide a random access mechanism and a dynamic preamble set adjustment mechanism which can enhance the probability that wireless devices perform a random access procedure successfully, especially for UEs having instant data transmission requirement, in a case where the number of wireless devices continuously increases, and further prevent radio resources in the base station from becoming idle, is an urgent need in the art and in the industry.